7r-Inductive effect

Three aspects of the inductive effect have to be considered 1,3,76,140 the (r-inductive effect, the inducto-electromeric or 7r-inductive effect, and the direct field effect. The first of these is the one most frequently... 

The problem of electrophilic substitution into the anilinium ion has been examined by the methods of m.o. theory. Attempts to simulate the 7r-inductive effect in Hiickel m.o. theory by varying the Coulomb integral of C(d (the carbon atom to which the NH3+ group is attached) remove 7r-electrons from the o- and -positions and add them to the... 

Ingold introduces the terms substrate field effect and reagent field effect to describe those aspects of the direct field effect numbered (2) and (3) in 9.1.2. His description of the substituent effect of the trimethylammonio group is thus given substantially in terms of the substrate field effect and the 7r-inductive effect, i.e. it is an isolated molecule description. The reagent field effect is seen to be significant in nitration and to produce qualitatively the same... 

The second 7r-inductive effect is the field effect, ittf, which arises through polarization of the whole 7r-system due to the electric dipole of (CH2)n Y, as shown in 1. 

The foregoing resonance structures describe the influence of the substituents on the 7r-electron distribution in the thiophene ring. Besides this effect the inductive effect of the substituents on the a-electi on system must be considered when discussing physical and chemical properties of thiophenes. 

This is essentially a method of providing an alternative set of 07 and or parameters for use in the DSP equation or EH equation. In the mid-1960 s Exner94 found evidence that the inductive effect from the para position of benzoic acid was stronger than that from the meta position by a factor of 1.14. He also suggested that 07 values current at that time and based on alicyclic and aliphatic reactivities were out of scale with am and ap by a factor of 1.10, and should be multiplied by this to introduce the 7r-inductive component. This led Exner to a revised analysis of am and ap in terms of inductive and resonance components. He calculated revised 07 values by multiplying the alicyclic/aliphatic values by 1.10, and then multiplying these further by 1.14 before subtracting from ap values to obtain revised values of or. 

A free radical is stabilized by an X substituent (Figure 13a) through a two-orbital, three-electron 7r-type interaction. The nucleophilicity of the radical is greatly increased. The X -substituted free radicals are more easily oxidized. The n effects of X substitution are somewhat augmented by the inductive effect of the electronegative X in stabilizing the radical. 

The actual structure is somewhere in between, i.e. (21 ab) a hybrid of which (21a) and (216) are the canonical forms. There will also be an inductive effect, as shown in (21a6) but this will be much smaller than the mesomeric effect as a electrons are much less polarisable, and hence less readily shifted, than 7r electrons. 

Kaufman and co-workers have made similar calculations and have shown that in covalent NF2 compounds there are no orbitals available on the nitrogen having energies low enough for significant 7r-bonding with the unshared electrons on the fluorine atoms (12, 13). In a series of X-NF2 compounds, the relative electron distributions are thus a function of the inductive effects of the X group. The various situations are envisioned as follows ... 

---